This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Currently, radiofrequency (RF) switches are used to combine multiple RF filters so that a single input or output can be used. One problem with switch based solutions is that one signal at the time can be connected to the output signal path. To address this problem, diplexers and duplexers have been developed which combine two input signals to generate one output signal. Diplexers can be extended to triplexers, which combine three input signals into a one output signal.
A diplexer is a passive device that implements frequency domain multiplexing. Diplexers are generally considered to be dual port, single throw devices. Two ports L and H (e.g., at which low frequency and high frequency signals are applied) are multiplexed onto a third port S. The signal to the common third port is thrown from the first port and from the second port. The signals on ports L and H occupy disjoint frequency bands. Consequently, the signals on L and H can coexist on port S without interfering with each other.
The diplexer, being a passive device, is reciprocal. The device itself doesn't have a notion of input or output. In the example above, the low frequency portion of a signal input to the third port S is thrown to the first port L and the high frequency portion of that same input signal is thrown to the second port H for output from the diplexer. Regardless of direction of signal propagation through the diplexer, the single common port S denotes it as a single throw device since the signal portions that are ‘thrown’ to ports L and H are from that common ‘throw’ terminal S. Diplexers differ from passive combiners or splitters. The combiner is not frequency selective. There also a power “loss” issue—a combiner takes all the power delivered to the S port and equally divides to the remaining two ports. A diplexer does not split power. A diplexer multiplexes two ports onto one port or vice versa, and is commonly used in frequency domain duplex (FDD) systems.
It is known to extend the diplexer concept to larger numbers of ports to multiplex. A three-port to one-port multiplexer is also known as a triplexer. The triplexer structure combines three inputs into one common output and so is a triple pole, single throw device. Triplexers are used in wideband code division multiple access (WCDMA) band I and VI. A further extension is the quadplexer, which combines four inputs into one common output as a quad pole, single throw device
These filters may be seen to have the form (n)pst in which (n) indicates the number of poles and ‘st’ indicates a single throw filter, or in alternative terminology they are single output n-input filters. In order to design such filters, they all need to be designed at the same time with a joint optimization. This is due to fact that all filters are interconnected to each other since those are sharing a common output port. This is a difficulty in implementing such filters in practice.